Workers are seen inside a Foxconn factory in the township of Longhua in the southern Guangdong province. Photograph: Bobby Yip/Reuters

A report into working conditions at Chinese factories operated by an Apple supplier has revealed "serious" labour violations, including excessive hours, unpaid wages and major health and safety risks.

The Fair Labor Association (FLA) said employees at Foxconn, which produces products including iPhones and iPads, typically worked more than 60 hours a week during peak periods but were paid unfair compensation for overtime.

Around two-thirds of workers told investigators that their take-home pay was insufficient to meet basic needs.

In addition, 43% said they had witnessed an accident at work, leading to fears of poor safety provisions at the plants.

Foxconn pledged to cut hours, protect pay and improve conditions in light of the month-long audit, which Apple ordered amid negative publicity over the plight of Chinese workers at the plants.

Conditions of 35,500 employees at three factories were investigated as part of the report.

In addition, there was a "widespread sense of unsafe working conditions" at the three plants, auditors found.

The FLA said it had secured "ground-breaking commitments" by Foxconn to address their concerns.

In a statement, Apple said: "Our team has been working for years to educate workers, improve conditions and make Apple's supply chain a model for the industry, which is why we asked the FLA to conduct these audits."